Directing beams of light in specific directions has many applications, and many technologies exist that can accomplish this task. Light, also known as radiation may be composed of a broad distribution of wavelengths, such as white light, or may be a very narrow band of wavelengths, such as produced from a typical laser. The wavelengths that compose light may be in the visible range, detectable by our eyes, or outside the visible range. Light just beyond the visible range on the long wavelength side of the spectrum is known as infra-red radiation. Light just beyond the visible range on the short wavelength side of the spectrum is known as ultra-violet.
Beams of light may be directed by various means, but directing light by means of a reflecting, movable surface, or mirror, is the most relevant to the present invention. A technology that can provide a reflective surface, and move that reflective surface in a controlled, high speed manner can find application in uses such as microscopy, projection displays, laser sensors, and similar technologies.
There are a number of actuation technologies known in the prior art, when coupled to reflective mirrors provide controlled beam steering.
There are a variety of methods for actuation that utilize electromagnetic effects. One method of directing light in a controlled manner at high speeds uses an electromagnetic device known as a galvanometer. This technology uses permanent magnets and/or ferromagnetic materials with electrical coils. Electrical current driven through the device initiates motion that can be controlled in a closed loop or open loop manner. This actuation technology coupled to a mirror can provide a high speed mechanism to control and direct light.
It has been observed that galvanometer based technology consume significant electrical power under operation, making them incompatible for applications where electrical power is constrained. It has been further observed that the mechanical complexity of the construction of galvanometer technology limits the ability to miniaturize this technology at low cost.
Light can also be directed in a controlled manner using mirror systems driven by voice coil motors. Voice coil motors are a simple electrical device, which are similar to a galvanometer, and sometimes also called a solenoid. Electrical energy applied to the windings drives a core linearly, driven by magnetic repulsion. Voice coil motors coupled to the edges of a mirror can be actuated in a controlled manner to tilt the mirror and effectively direct light.
It has been observed that voice coil mirror systems consume significant amounts of electrical power, and given that they have multiple parts including fine electrical windings, they are difficult to miniaturize at low cost.
Another technology that uses reflective surfaces for directing light in a controlled manner is electrostatic actuation. This technology uses that fact that when voltage is applied across two surfaces at close proximity, positive and negative charges collect on the respective surface, and an attractive force is generated. This actuation effect can applied in a beam steering technology by using the force generated, and the resulting motion of attractive surfaces to change the angle of a mirror.
It has been observed that electrostatic actuation results in small movements, which in turn, even when mechanically amplified into larger angles, results in modest angles of motion in the mirror.
Piezoelectric effects also can be coupled to a mirror for beam steering. Certain materials expand when subject to high voltages, in a process known as the piezoelectric effect. It has been observed that mirror systems driven by piezoelectric effects, similar to electrostatic actuators, deliver multiple angles of motion in the mirrors.
Electrothermal actuation can be used to drive controlled angular deflection in mirrors. This class of device takes advantage of the fact that most materials expand in length when heated. By careful design, electrical power can be dissipated selectively in electrothermal actuators to produce bending or linear extension. This motion can then be coupled with mirrors to deliver a beam steering effect.
It has been observed that electrothermal actuators are relatively slow, and do not produce high speed precision motion relative to other technologies. Additionally, they typically consume significant electrical power in order to generate the high temperatures in regions of the actuators. In order to produce high temperatures and the associated thermal expansion more efficiently, some package the actuators in vacuum or low thermal conductivity gases, adding to the cost of the product.
The aforementioned actuation technologies that allow for the controlled steering of light can be realized using several different manufacturing technologies. These technologies can be manufactured by traditional means, including machining, electrical winding, and hand assembly. Additionally, these beam steering technologies can be realized using semiconductor-like fabrication technologies, known as Micro-Electro-Mechanical Systems (MEMS).
As these devices are miniaturized, typically the actuation speeds that can be realized increase. It has been observed that traditional manufacturing methods do not scale down to small sized cost effectively. MEMS manufacturing technology has the capability of forming high precision mechanical structures at sub mm scales, but it has been observed that the beam steering devices manufactured using MEMS fabrication, even when produced on large silicon wafer, do not achieve sufficiently low cost in high production volume. This is generally due to the complexity of each manufacturing step, the number of manufacturing steps, and the complex equipment used.